This invention relates to metal salts of phosphorus acid esters and more particularly, to a simplified method for the preparation of such compounds wherein separation of reaction by-products is facilitated.
Metal salts of phosphorus acid esters are known compounds which find use in a number of applications such as additives for hydrocarbon fuels, unsupported catalyst components for the polymerization of alpha-olefins, and materials useful in the preparation of unsupported alpha-olefin polymerization catalysts. Additionally, as disclosed in our copending application Ser. No. 973,108 filed in the name of Glen R. Hoff and Peter Fotis on the instant filing date, we have found that divalent metal salts of phosphorus acid esters give highly beneficial results when used as support materials in the preparation of highly active supported catalyst components for the polymerization of alpha-olefins.
A number of methods for the preparation of metal salts of phosphorus acid esters are known. One such method involves reaction of phosphorus acid esters and metal halides. Thus, for example, cobalt and nickel bis(diethyl orthophosphates) have been prepared by reaction of triethyl orthophosphate with the divalent metal chlorides as reported in Paul, R. C., et al., Chem. Abs., Vol. 77 p. 334 (1972). Similarly, dialkyl orthophosphate salts of various Group IA, IB, IIIA, IIIB, IVB, VB, VIB, VIIB, and VIII metals have been prepared by reaction of metal halides with trialkyl orthophosphates as reported in Mikulski, C. M., et al., Chem. Abs., Vol. 80, p. 518 (1974). Reaction of anhydrous vanadium trichloride, chromium trichloride, manganese dichloride and copper dichloride with triethyl phosphate to form bis- and tris(diethyl phosphate) salts also has been reported; see Paul, R. C., et al., Chem. Abs., Vol. 82, p. 597 (1975). U.S. Pat. No. 3,910,976, to Fein, discloses reaction of magnesium chloride hexahydrate with tris-2-chloroethyl phosphate to form magnesium bis(di-2-chloroethyl phosphate). Mikulski, C. M., et al., Chem. Abs., Vol. 75, pp. 485-6 (1971), discloses reaction of trivalent vanadium, chromium, and iron halides with triethyl thionophosphate to form tris(diethyl thionophosphate) salts of the metals.
A related method, disclosed in U.S. Pat. No. 3,401,184, to Revukas, involves reaction of phosphorus pentoxide with halides of polyvalent Group II, IV, VI, or VIII metals and hydroxyl group-containing organic compounds in an organic solvent.
While the above-described preparative methods give the desired products, the use of metal halides as starting materials often is disadvantageous because such materials typically are difficult to dry and maintain in anhydrous condition. As a result, water often is present in the final products. Further, the use of metal halides as starting materials leads to formation of hydrogen halides and/or organic halides as reaction by-products. The presence of such by-products and/or water in the final products renders the same unsuitable for a number of applications. For example, the presence of water in the phosphorus acid ester salts used as support materials in the preparation of highly active alphaolefin polymerization catalyst components according to our copending patent application results in inferior catalyst components because water poisons the activity of the components. Similarly, the presence of even traces of hydrogen halides in certain phosphorus acid ester salts used as lubricant additives is harmful. Although water and reaction by-products can be removed from phosphorus acid ester salts prepared according to the above-described methods by suitable drying and washing techniques, such operations add cost and complexity to the preparation.
To avoid the above-described difficulties, it has been proposed to prepare metal salts of phosphorus acid esters without the use of metal halides as starting materials. For example, U.S. Pat. No. 3,422,126, to Bauer discloses that halogen-free titanium tetrakis(mixed mono- and dialkyl orthophosphates) can be prepared by reacting tetraalkyl titanates with mixed mono- and dialkyl orthophosphates. Aliphatic alcohols are the primary reaction by-products and are removed by carrying out the preparation at temperatures high enough to distill the alcohol. Similarly, U.S. Pat. No. 3,929,745, to Huerta et al., discloses reaction of vanadium pentoxide or alkyl vanadates with organic phosphates, optionally in the presence of oxygen, to form vanadium oxybis(organo phosphates). Primary reaction by-products include alcohols, ethers, aldehydes, and water. U.S. Pat. No. 3,474,080, to Rekers discloses preparation of chromyl bis(diorgano phosphates) by reacting chromium oxide with triorgano phosphates. U.S. Pat. No. 3,669,945, to Nakaguchi et al. discloses reaction, either in the presence of water and/or alcohol or neat, of vanadium compounds such as oxides, sulfate, oxysulfate, sodium and ammonium salts of vanadic acid and esters thereof with alcohols, as well as halides and oxyhalides, with phosphoric acids, their anhydrides, salts, and esters. Similarly, U.S. Pat. No. 3,427,257, to Bayer et al., discloses reaction of vanadium oxides with organophosphorus compounds of the formula O.dbd.PR.sub.1 R.sub.2 R.sub.3 wherein R.sub.1, R.sub.2, and R.sub.3 are hydrogen, hydroxyl, alkyl, alkoxy, or aryl, at least one of R.sub.1, R.sub.2 and R.sub.3 being an organic group.
Another preparative method which avoids the use of metal halide starting materials is disclosed in U.S. Pat. No. 3,910,976, to Fein, wherein tetravalent vanadyl salts, such as vanadyl sulfate, oxalate, or acetate, are reacted with Group IIA or IIB metal organo phosphate or organo phosphite salts to form vanadium oxybis(organo phosphates) or oxybis(organo phosphites) by metathesis of the metals contained in the starting materials.
While the above-described methods avoid the formation of halogen-containing reaction by-products, other difficulties are encountered. For example, the alcohols and/or ethers formed as by-products according to the Bauer and Huerta et al. patents tend to complex with the final products such that substantial removal of such by-products often is difficult. Similar to water, alcohols and ethers can adversely affect the performance of alpha-olefin polymerization catalysts. The metathesis preparation disclosed by Fein it disadvantageous because the starting materials employed include compounds of the type to be prepared and because incompletely reacted starting materials are difficult to remove from the final product.
From the foregoing, the desirability of producing metal salts of phosphorus acid esters by a method which avoids the use of metal halides as starting materials and permits substantial removal of by-products by convenient means can be appreciated. It is an object of this invention to provide such a method. A further object of the invention is to provide for the preparation of metal salts of phosphorus acid esters useful in the preparation of alpha-olefin polymerization catalyst components. Other objects of the invention will be apparent to persons of skill in the art from the following description and appended claims.
We have found that the objects of this invention can be attained by reaction of metal salts of organic acids with phosphorus acid esters. The metal salts employed as starting materials are easy to dry and maintain in the anhydrous state such that impurities are substantially excluded from the preparative system and the final products. Moreover, the primary by-products produced according to the invented method are organic acid esters which are conveniently removed by techniques such as distillation, filtration, decantation, and through the use of reduced pressures. While the by-products are capable of complexing with certain of the final products, the complexes are sufficiently weak that substantial removal can be achieved by such techniques. According to a particularly advantageous embodiment of the invention, the metal salts and phosphorus acid esters employed as starting materials are selected such that low boiling organic acid ester by-products are formed. Such by-products can be removed during preparation through the use of suitable reaction temperatures, and production rates are thereby increased.